Jessica Lowndes (aka 90210's resident druggie, Adrianna) dressed up as an adorable Minnie Mouse, while Ryan Eggold (the hunky teacher) used the night as an excuse to dress in drag.

We're not quite sure what Shenae Grimes went as, but she looked hot and we love her anyway. However, her guy pal is totally killing her street cred - couldn't he have found a more um, original costume than a pumpkin vest over a plain white tee shirt?